Shaun Anthony Lacey, 32, pleaded guilty to a single count of causing grievous bodily harm over an incident in the early hours of October 28, 2018 and was sentenced to 27 months imprisonment, to be served in the community through an intensive correction order.

On top of the intensive correction order, Lacey will also have to do 240 hours of community service work over the next 12 months.

In his judgment, Justice Michael Elkaim made note of the "participation (but not necessarily culpability) of Mooseheads in an inordinate number of offences in the ACT".

On the night in question the victim left Mooseheads at about 3.40am with friends, on his way to a nightclub, when he asked a group of men, of which Lacey was one, for a light for his cigarette.

Another member of the group teased the victim by holding a lighter very close to his skin, after which the victim pushed the lighter away, and the other man slapped the victim, who then pushed the other man from behind.

According to the statement of agreed facts, Lacey followed the victim and punched him in the jaw. The victim lost consciousness and fell to the ground.

Lacey then went to Mooseheads, "not surprisingly," wrote Justice Elkaim in his judgment, but a security guard was told what happened, who brought him to the front of the venue to wait for police.

The victim was found unconscious by police, with blood coming from his mouth.

Justice Elkaim wrote in his judgment that when questioned by police Lacey "made a weak attempt at justification by saying 'He got right up in my face, so I hit him'".

The victim suffered a moderate to severe brain injury, brain bleeds and a hairline base skull fracture, spending 25 days in hospital before an extensive period of rehabilitation. He now lives with an acquired brain injury.

"Its effects will probably stay with him for the rest of his life; all of this because the drunken offender could not contain his temper and, for no good reason, attacked the complainant," Justice Elkaim wrote in his judgment.

According to a speech pathologist's report from August this year, the victim has returned to work at a hotel and has been promoted to working as a receptionist, and has achieved some goals around word finding difficulties. A letter from the victim's parents was also tendered in court.

It said the victim was "still the friendly, good natured kid that he has always been," but the assault had made him less trusting of others and the unknown.

"Whereas previously everybody was his friend or potential friend, he treated everyone with acceptance and kindness. This has faded since the assault with [the complainant] being more cautious and non-trusting," the letter from the parents said.

Lacey was subject to a good behaviour order at the time of the offence, and had previous convictions in both the ACT and NSW, including for common assault. The judge noted that he was a binge drinker and that alcohol led to criminal behaviour, but he has not consumed alcohol since the offence.

Justice Elkaim said Lacey had been assessed as having a low to medium risk of general re-offending, and understood the seriousness of his behaviour.

In sentencing remarks, Justice Elkaim said deterrence was an important consideration and the community is gravely concerned about the prevalence of one-punch attacks by young men fuelled by alcohol, but recognised the offender had good prospects of rehabilitation and had made attempts to deal with his alcohol problem.